The present invention relates to an improvement in personal computers which permits the use of a plurality of CRT displays each capable of displaying ASCII characters, ideographic characters such as those of the oriental languages, or a mix of ASCII and ideographic characters.
In recent years the personal computer has found widespread use in offices for performing various functions such as word processing. This use has created a need for multiple stations, each including a keyboard and a CRT display so that multiple operators may simultaneously use the word processing capabilities of the personal computer. This need has in part been satisfied by software. However, the software approach places a heavy burden on the personal computer. According to one feature of the present invention, display control cards are provided, each being insertable into a slot in the motherboard of the PC and each having connector means to which a keyboard and a display may be connected. When it is desired to add another station to a system, all that is required is that another display control card be inserted into an empty slot on the motherboard in the personal computer, and the keyboard and CRT display comprising the new station connected to the card.
Word processing in oriental languages presents certain problems because of the large number of characters in the languages. For example, the Chinese language comprises thousands of ideographic characters. One must know about 2,000 of these characters to be considered literate and one is considered well educated if he has a written vocabulary of 5,000 characters. In an effort to deal with the problem certain standard codes have been adopted for certain languages. For example, the de facto standard GB2312-80 code is widely used for the Chinese language. The GB2312 standard may be visualized as a matrix of rows and columns of characters. Each character of the font is assigned a 16-bit code wherein the first byte designates the column location and the second byte represents the row location of the character in the matrix With a 16-bit code it is possible to define 2.sup.16 or 65,536 characters. However, the standard assigns a specific 16-bit code to only about 7600 characters and the assigned code point values do not comprise a sequence of consecutive numbers In other words, the code set is loosely populated and certain locations in the matrix do not represent any character. Therefore, if the 16-bit code is used to directly address a ROM in order to read out the digital video representation of a character, as is conventionally done, an extremely large ROM is required, with less than one-eighth of the ROM being used to actually store the digital video representations of the characters. A similar situation exists with respect to the Japanese Interchange Standard (JIS) except that the locations in the matrix which do not represent any character are different. A feature of the present invention is the provision of a translator ROM which is addressed by a numeric value designating a particular character in a given code to produce an address value which falls within a range of consecutive numbers, the address value then being utilized to read from a font ROM the digital video signals which are applied to a CRT to display the character.
In oriental languages the characters representing names are frequently fanciful. Also, it is desirable to be able to provide a font of special characters which might be required in a specific system application. It is not feasible to provide ROM storage of the digital video representation of all such special or fanciful characters. Therefore, a further feature of this invention is the provision of a loadable font memory the contents of which may be changed by the user as he wishes to provide representations of special characters required for a specific job application.